Certain water-thinnable coating compositions composed of acidified addition copolymers containing pendent carboxyl groups and pendent aminoester groups formed by aminoethylating pendent carboxyl groups with an excess of alkylenimine and epoxy resins are known, as shown by U.S. Pat. No. 3,719,629 to Martin et al., issued Mar. 6, 1973. These acidified copolymers are cationic acid salts, i.e., the salt groups are provided by reacting basic groups with an acid. This creates a number of serious disadvantages. For example, because of the cationic nature of the copolymer, it cannot be readily formulated into a coating composition by blending it with the conventional anionic modifiers normally employed in coating compositions, acid sensitive pigments such as the carbonates cannot readily be employed, and the conventional anionic pigment dispersants cannot be utilized in the usual manner. Another disadvantage, due to the fact that the copolymer product is an acid salt, is that it cannot be satisfactorily employed as a coating material for unprimed metal substrates since such acid salts usually cause flash rusting.
Water-based coating compositions containing basic salts of polycarboxylic acid resins containing amine groups formed by iminating a portion of the carboxyl groups are shown by U.S. Pat. No. 3,494,847, issued to Yurcheson et al. on Feb. 10, 1970. The coating compositions disclosed in U.S. Pat. No. 3,494,847 generally utilize as the polycarboxylic acid resin certain fatty acid adducts containing unsaturation for curing, but in some cases interpolymers of acrylic and other vinyl monomers, at least one of which contains a hydroxyl group, are contemplated. In such cases, the interpolymer is cured with an amine-aldehyde condensate to which may be added a polyepoxide.
U.S. Pat. No. 3,945,963, issued to Levine et al on March 23, 1976, described emulsions of acrylic interpolymers in combination with certain resins derived from epoxides. These resins are either very high molecular weight (above 20,000) or defunctionalized (and thus not a polyepoxide) by reaction of the epoxy groups, such high molecular weight or defunctionalization being necessary in order to provide the one-package compositions contemplated.